Every word has a certain meaning and the meanings of words are not always permanent. One of the words evolution situations is the expansion of the words meanings. When you attend to Chinese school to study Mandarin, teachers would tell you that the words meanings expansion is the change from the small range to the large scope of the objective things. That is to say, the extents of the objects summarized by the old words are expanded. Or we can say the meanings expressed change from the individual meanings into the general meanings.
After such kind of expansion, the meanings scope becomes much larger than before. In order to understand it better, the following examples are provided to explain. The word 健康 originally means people’s physiological functions are normal and without imperfections or disease. Then, it can be expanded to indicate that things have normal conditions. For instance, we can say 思想健康. Originally, the meaning of肉was the meat of the birds and beasts. After expansion, the 肉 we mean today can be the meat of every living thing. In this way, the former meaning of 肉 is disappeared.
If you have been studying in Chinese language school in China for a long time, you should have known that the meaning of 江and 河represents Yangtze River and Huanghe River respectively in ancient China. They were proper noun at that time, but they carry the meaning of indicating all kinds of rivers in modern Chinese language. In ancient times, 睡 meant doze only while it means to go to sleep at present. The ancient people call “sleep” as 寝.
You may know the word水分 which originally meant the water contained in things while we can use it to indicate the unreal, unnecessary compositions or the elements added such as 文章要提炼水分，力求精简. Besides, 雄 and 雌 were only for the gender of birds while indicate that of all kinds of animals.
By this token, when the meaning of certain expanded, the expanded meaning includes the original meaning. One thing that the foreign learners who study in China should know is that the reason of words meanings expansion is the developing knowledge of human beings. Since people know more things, they conceptualize the specific things, forming the change from specific to general and the part to whole.